Well, that's stretching it a bit, Jim.

A local club-sponsored Q500 event allows only sport .40 engines with stock mufflers, and 15% nitro. Thunder Tiger .40's are typically turning 9X7 APC props over 17K RPM on the ground. An APC 9X7 at 17K will generate over over 101 dBA at 9 ft, no matter what is turning it. That's about the lower bound on .40 glo-powered pylon racers. With a Nelson turning a 7 inch prop at over 30K, the level can exceed 120 dBA @9 ft. They sound loud because they darned well are loud.

It is true that 4-strokes often put out more physical noise power than 2-strokes producing the same shaft power, and that is easily confirmed (when exhaust noise is dominant) by using the C-scale on the meter, which is essentially flat frequency response. With the A-scale selected, the physical level sensed by the meter is frequency weighted to emulate human hearing response. The weighting curve is quite steep in the usual frequency range of exhaust pulses from our model engines, and the 4-stroke emits them half as often. It is not unusual for a 4-stroke to measure higher on the unweighted scale, yet measure lower on the A-weighted scale that models human perception.

Higher frequencies may seem more abrasive at the same perceived levels, but if so the effect isn't enough, or isn't regular enough in statistics derived from countless field surveys, to be included in environmental quality standards promulgated by ISO, ANSI, HUD and many other such agencies. Virtually all such standards are based on frequency-weighted level measurements, and almost all agree on the A-weighting scale. These standards are what local ordinances are traceable to, and if you are called to respond to a noise complaint, what counts is what is written in the ordinances.

Abel